<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        function getWeek(number){
            var now = new Date();
            var day = now.getDate();
            var weeks = new Array('星期一','星期二','星期三','星期四','星期五','星期六','星期日');
            var real_number = (number + day) % 7;
            var week = weeks[real_number-1]
            return week;
        }
        number = parseInt(prompt("请输入一个天数"));
        alert(number + "天后是"+getWeek(number));
    </script>
</head>   
<body>
    
</body>
</html>